The addition of armor to an automobile or other vehicle very substantially increases its weight, thereby requiring that the vehicle frame be reinforced in critical areas to carry the added weight. The armoring of vehicle doors especially stresses the frame because the doors are cantilevered from hinges along the door edge. An armored door is also subject to a very large, abrupt force if it is thrown open or slammed shut. Such stresses tend to cause the door to "sag" relative to the door frame.
The door structure and hinges as supplied by the original vehicle manufacturer are often used by the armorer, with some modification to carry the additional load. Steel or other armor panels are installed between the original inside and outside "skins," panels or liners of the doors; the door skins themselves are not necessarily made heavier to carry the armor. Usually armor panel mounting brackets are attached to the inside of the metal outer skin, and the armor panel is "hung" or suspended from the door structure by such brackets. The weight of the armor panel and the bulletproof glass is typically carried by the door skin, to the door edge to which the hinges are secured.
Experience has shown that the relatively thin gauge metal used for door outer skins (e.g., 18 or 20 gauge) tends to sag under the weight of the armoring, even if so-called lightweight or composite armor is used. The sagging tends to occur progressively with time as the door is repeatedly opened and closed in use; a door which was properly aligned with respect to the frame at the time the vehicle left the shop, gradually becomes increasingly disaligned. At the least such sag is unsightly and undesirable; and ultimately it can prevent closing and latching. Correcting the sagging, once it has occurred, requires realignment and "shimming" (inserting thin spacers between the hinges and their mounts, to return the door to a position of alignment). Such adjustments are inconvenient, specialized, and in any event difficult because of the weight of the door. The door must be supported while the hinges are loosened and one or more shims inserted to correct the sag.
It is therefore desirable to provide an armored door assembly which will be less subject to sagging in use.